Whether it’s not being able to live-stream your latest tech unboxing or suffering the indignity of being rendered unable to stream music on your commute to work, there are plenty of reasons why phone batteries running flat are the absolute dirt worst. As hard as it is to believe, however, there are situations in which a phone running out of battery is even more devastating than making us endure a boring subway ride to the office.

A few examples: A firefighter needing guaranteed communication with his or her colleagues; a person trapped following a natural disaster and needing to call for help; or a person in the developing world with limited alternate means of staying in touch with family.

Fortunately, that’s where researchers from the University of Washington can help. They’ve invented a prototype cell phone that requires no batteries; instead harvesting the few microwatts of power it needs to run from ambient radio signals — or even light.

“The reason we chose to build a battery-free phone is because phones are one of the most important devices that virtually everyone uses,” Vamsi Talla, a former UW electrical engineering doctoral student and Allen School research associate, told Digital Trends. “Most of us have experienced the situation where our phone battery has died at an inopportune time, such as when we want to make an important phone call.”

The battery-free cell phone saves on power by taking advantage of analog, as opposed to digital, voice encoding. The device’s range comes from tiny solar panels called photodiodes.

Talla said that there are two directions for the project from here. One is to license the technology to existing smartphone makers who could incorporate it into their devices so that emergency calls can be made, even if your iPhone or Samsung Galaxy is out of juice. “That could be a real lifesaver,” Talla explained.

The other direction is to build on the existing prototype to make bare-bones phones that could be used by people who might not otherwise have the luxury of being able to charge their handset whenever they want. “A phone like this would never need to be recharged, and could still be used to make phone calls and send text messages,” Talla said.

At present, the phone is extremely basic — comprising off-the-shelf components on a printed circuit board. Talla said that future versions could be more advanced, though.

“This is the first-generation model,” he said. We’re going to add more functionality in the future. The goal is to make a fully functional smartphone.” Future improvements, he said, could include the same kind of low-power display technology used in Kindle e-readers, as well as a low-power camera.

A paper describing the technology is published in the latest issue of the journal Proceedings of the Association for Computing Machinery on Interactive, Mobile, Wearable and Ubiquitous Technologies.